The present invention pertains to a device to be lubricated with a lubricant protection arrangement, as well as to a corresponding lubricating method.
The lubrication of machine elements with lubricants such as different types of grease, oil or solid lubricant fulfills different functions. On the one hand, it serves for preventing or reducing wear phenomena at contact points between so-called friction partners, for diminishing stress concentrations, for example, in rolling bearings and for reducing additional frictional shearing stresses on surfaces. Lubricants are furthermore used for corrosion protection and for cooling machine elements if a sufficient lubricant exchange and therefore a corresponding dissipation of heat can be ensured.
The objective of lubrication consists of separating contacting surfaces of the friction partners by means of a hydrodynamic liquid film or a protective reaction layer. In the hydrodynamic formation of lubricating films, an elastic deformation frequently also plays an important role such that one refers to so-called elastohydrodynamic lubrication in this case. The main objective of lubrication is a complete separation of the friction partners. This can be achieved with a suitable combination of the lubricant viscosity, the moving speed of the friction partners and the contact pressure, as well as corresponding constructive adaptations.
As mentioned above, different types of lubricating oil, lubricating grease and solid lubricant are used as lubricants. This application mainly focuses on liquid lubricants such as, e.g., lubricating oils. Important parameters of lubricating oils that can be influenced are the density, the viscosity index, the shear stability, the so-called Cloud-and-Pour point, the neutralization capacity, the neutralization value, the total base number and the flash point. Furthermore, the thermal capacity, the air absorption capacity and the content of water and foreign matter influence the properties of a lubricating oil.
Various types of lubricating oil additives are known for modifying tribologically relevant lubricating oil properties, for example, the viscosity/temperature behavior and/or the frictional and wear behavior, as well as for improving the oxidation resistance or the prevention of foaming.
Additives may be added to lubricating oil in the form of commercially available so-called additive packets. In modern motor oils, 10 to 20% of the overall volume consists of additives. Polymeric additives typically form another 3% of the overall volume.
The service life of lubricating oils is limited. Due to interactions with the system to be lubricated and the surrounding atmosphere, the service life of the lubricating oil and of the entire tribological system can be significantly reduced. In this context, oxidation processes that lead to an increase of the neutralization value and therefore an increased corrosiveness of the lubricating oil are considered particularly critical. An increase of the viscosity causes the tribological properties of the system to change over time. Deposits formed due to corrosion by separating lubricating oil components can cause blockages. A loss of additives can result in certain components of the lubricating oil no longer being sufficiently protected such that its quality deteriorates. Consequently, frequent oil changes or maintenance intervals are required.
It would therefore be desirable to increase the service life of a lubricating oil or, more generally, a liquid lubricant, particularly a lubricating oil that is based on minimal oil.